The present invention relates to semiconductor structures and, more particularly, to structures for preventing dicing damage on photonics wafers.
Silicon photonics chips are being developed for high speed interconnects between dies. Waveguides can be built on silicon on insulator (SOI) wafers and can be integrated with CMOS devices. In order to make such integration, though, a connection must be made between an “off-chip” optical fiber and the waveguide structure, itself. Out-of-plane coupling uses an optical grating to couple light from the optical fiber to the waveguide structure, but this limits the optical signal to one wavelength. In-plane coupling, on the other hand, allows broadband transmission (multiple wavelengths, and therefore higher bandwidth). However, achieving high coupling efficiency with in-plane coupling is difficult.
A reason for loss for in-plane coupling is that the core of the optical fiber has a much larger diameter than the Si waveguide structure. The loss can be reduced using a groove or channel underneath the Si waveguide, for improved coupling. However, the inventors of the present invention have found that the groove results in a thin membrane that is easily damaged during dicing. By way of experimental results, it has been found that due to water jet pressure during dicing and rinsing, damage to the waveguide structures results at the thinned membrane. When water jet pressures are lowered to the minimum possible pressures in which dicing progress can support, there was still breakage of the membrane, albeit to a lesser extent. However, with the lowered water jet pressures, wafers become contaminated with Si dust which can affect assembly, reliability and optical coupling.